Photonic crystals are known to provide wavelength-dependent filters, beam splitters, mirror components, and right-angle waveguides. For example, reference may be had to A. Mekis, et al, "High Transmission Through Sharp Bends in Photonic Crystal Waveguides", Physical Review Letters, V. 77, N. 18, Oct. 28, 1996, pp. 3787-3790, and to H. W. P. Koops, "Photonic Crystals Built by 3-Dimensional Additive Lithography Enable Integrated Optics of High Density", in Photorefractive Fiber and Crystal Devices: Materials, Optical Properties, and applications II, (F.T.S. Yu, S. Yen, Editors) Proceedings Society Photographic and Instrumentation Engineering, Volume 2849, August, 1966, pp. 248-256. Because photonic crystals are on the order of several wavelengths in each of two major dimensions, and are made with microprocessing techniques, optical processing systems employing photonic crystals can be extremely small, thereby permitting extremely high bit density and high rates of processing data.
A principal drawback, as is pointed out by Koops, supra, is the formidable problem of coupling light between waveguides and photonic crystals.